Since the introduction of the Personal Computer (PC), the microprocessor has interfaced with the system motherboard through a socket. The role of the socket is to provide electrical connectivity between the microprocessor and the motherboard, while also allowing tool-free installation, removal and interchangeability of the microprocessor without damage.
As microprocessor speeds have continued to increase, socket requirements are becoming more challenging. Power consumption continues to trend upward, driven by the increased leakage current of smaller silicon features, the increased dynamic current required to scale frequency, and the incorporation of multiple cores within a single package. At the same time, the required socket bandwidth to support the necessary high-speed signaling is also increasing rapidly.
Many microprocessor sockets used today are built around the pin grid array (PGA) architecture. Here, pins on the underside of the processor are inserted into the socket, usually with zero insertion force (ZIF). Newer socket designs use a land grid array (LGA) in which the pins are on the socket side instead and come in contact with pads on the processor. Thus, power and electrical signals may pass between the microprocessor and the motherboard via the socket.
Electrical interconnects may have their limitations. For example, currently planned electrical implementations of the common system interface (CSI) protocol links may be limited in the bandwidth distance product even at 6.4 gigabits/second (Gb/s). Among other things, CSI allows microprocessor cores to communicate with one another directly. The limitation imposed by the inadequate bandwidth distance product of electrical channels based on commercially available components and materials is currently solved by reducing the distance of the microprocessors in the multi-processor system or limiting system bandwidth. This is an unsustainable trend, however, and a better solution is desirable.